Soldiers and police in Brussels allegedly held an orgy while their colleagues hunted for terror suspects.

Eight soldiers and two female police officers allegedly engaged in lewd acts at a police station in the Ganshoren part of the city, just north of Molenbleek, where the hunt for suspects linked to the 13 November terror attacks has focused, Belgium's Le Derniere Heure reported.

With the threat level raised to four, the country's highest level, on November 21, the city was placed on lockdown, with restaurants, schools, museums, and the city's metro system all closed down.

Police spokesman Johan Berckmans told local media that 15 to 20 soldiers had been based at the station over a two week period in late November, who stayed in a dormitory so as not to have to make the journey back to army barracks at night. He said an internal investigation had been launched into the allegations.

The Paris attacks are believed to have been planned by Belgian-Moroccan Abdelhamid Abaaoud. One of the alleged perpetrators of the attacks, Belgian Salah Abdeslam, remains on the loose.